Irish tourists who trashed a beach and threatened locals in New Zealand also allegedly caused havoc on their flight into the country.

Among the carnage were reportedly demands for large seats, continuous requests for alcohol and a dirty nappy left in an overhead bin.

One passenger on the Cathay Pacific flight from Hong Kong to Auckland on Friday told the New Zealand Herald the family made the journey the 'worst flight' of his life.

Before the flight departed, both children gallivanted around the plane's aisles and a daughter allegedly yelled at her mother who demanded food from staff, the passenger claimed.

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The Irish tourists who trashed and threatened locals on a New Zealand beach also allegedly caused havoc on their flight into the country

When others realised the family-of-six had apparently left a soiled piece of clothing in their hand luggage, the fellow passenger reached the end of his tether.

'The parents also asked for different seats because they are overweight and didn't have enough space, even insisting the attendant ask another couple with the only free seat on the plane to switch with them,' he said.

'They would lean against us often with an armpit on my head or an entire arm blocking the movie I attempted to watch. I was already boiling at this point, so asked the attendants if we could move.

'After leaving the plane they even left one of her [their baby's] suits in the overhead that we think had actual poop left in it, because it smelt like death.'

As the plane descended the passenger said the young girl ignored the seatbelt sign and attempted to stand.

Days later the supposed same group were filmed leaving beer bottles and rubbish on a busy beach, before a child threatened to 'knock the brains out' of locals who confronted them in now-viral footage.

Witness Krista Curnow said the group of about 12 tourists, who spoke with an Irish accent, turned violent when she asked them to clean their mess as they left the beach

The incident, which unfolded at Auckland's Takapuna Beach on New Zealand's North Island on Sunday, was captured on camera by Krista Curnow.

She said the group of about 12 tourists, who spoke with an Irish accent, turned violent when she asked them to clean their mess as they left the beach.

'Their response was basically if we have a problem then we can pick it up and that that's what the council is for,' Ms Curnow said.

'I approached the family to ask again if they could not disrespect our country while visiting and pick up their rubbish.

'Their response was basically if we have a problem then we can pick it up and that that's what the council is for,' Ms Curnow said